Problem: $ B = \left[\begin{array}{rrr}2 & 1 & 2 \\ 0 & 2 & 2 \\ 1 & 1 & 0\end{array}\right]$ What is $ B^{-1}$ ?
Solution: $ = \left[\begin{array}{rrr}\frac{1}{3} & -\frac{1}{3} & \frac{1}{3} \\ -\frac{1}{3} & \frac{1}{3} & \frac{2}{3} \\ \frac{1}{3} & \frac{1}{6} & -\frac{2}{3}\end{array}\right]$